Sorry but you are wrong. The purposes that ARINC list are only a small number of their uses. Their main use is for aircraft flying the oceans and deserts where HF is used instead of VHF because VHF doesn't have the range. Often 20-30 minutes can go by between reporting points and that's where the selcal comes in. It's basically like a paging system for aircraft. The aircraft gives the ground op the selcal code and once the ground op transmits the code to make sure it works, the aircraft can remove their head sets to save listening to the endless HF static and rest assured knowing that if the ground op needs to contact them s/he will do by selcalling them which will make a chime in the cockpit.

This is all covered in detail on my website at http://www.selcalweb.co.uk but very unusually there's currently a problem with my host and the site is showing as offline hence why I didn't list the address in my original reply.

I've been monitoring HF, tracking and tying up selcal codes to individual aircraft for over 40 years so strangely enough I do know what I'm talking about and also have a database with nearly 20,000 individual tied up selcal codes too.